Every project has its quirks – when some little problem throws up an odd aside from the main activity that requires investigation. Sometimes it turns out to be a red herring. Occasionally it throws up a challenge that changes the whole design.
I worked on the Advanced Passenger Train back in the 1970s. One day, someone asked the question, “What would be the effects on another train of the pressure pulse produced by a 250kph train entering a tunnel?” The APT itself had a valve to seal the air system when in a tunnel, but other trains didn’t. No-one knew the answer, so a small team was asked to find out.
Some six miles north of Derby, on the main line to Sheffield, is a one-mile-long straight tunnel, passing under the southernmost hills of the Pennines. One weekend, the line was closed, the three air shafts were blocked by large air bags and the fun began. Trains were raced between Derby and Ambergate, a similar distance north of the tunnel, and pressure readings taken as they passed through the tunnel. Some runs had stationary vehicles on the other line to measure the effect. The final runs used two trains timed to pass each other in the tunnel, after a few practice runs. The drivers certainly enjoyed themselves!
At that time, Derby had the last organ bellows maker in the country. A large box, big enough for two people to sit side by side, was constructed with Perspex sides inside a steel reinforced frame. The whole top of the box was a giant organ bellows driven by a hydraulic piston. Volunteers (including me) sat in the box while the pressure pulses recorded in the tunnel were reproduced, suitably scaled to a range of train speeds up to 250kph. Most found it very noticeable, while a few were uncomfortable. The next question was, “Is the pulse damaging hearing?”
"Physical sensations, please tick in the appropriate box - Painful, Discomforting, Disquieting, Very noticeable, Just noticeable, Not noticeable."
Images from the British Transport Film "E for Experimental".
One Monday morning, six of us had our hearing tested, then again on Wednesday morning. We then had a session in the box where our virtual train went through a series of tunnels at full speed. We had an immediate hearing test, followed by another on the Friday. One subject had a single ear-drum reversal, which meant it became convex, rather than the normal slightly concave. All of the ear-drums were pink, showing the effects of exercise. Immediately after the test runs, all six had improved hearing on test, probably due to the extra exercise on the small bones in the ear. All were back to normal on the Friday.
It was concluded that the pressure pulses caused no permanent impairment and were possibly marginally beneficial. Of course, in reality no unsealed train would have gone through a long series of tunnels at that speed, so the tests were extreme. The exercise had no effect on the design of the APT, but we had answered the question, learned something interesting – and we had some fun!
See also "Looking Back - the Advanced Passenger Train" by Colin Ledsome originally published in "Engineering Designer", the magazine of the Institution of Engineering Designers.
If you have any memories of working on the APT - Please let me know !